Loon chicks are hatching on New Hampshire’s lakes, and biologists are asking that people heading to the water for the July Fourth weekend leave the endangered birds alone.

Biologists say people should stay at least 150 feet away from adult loons and their chicks. Boat collisions are the greatest human-related cause of chick mortality and the third-highest cause of adult loon mortality, following lead poisoning or injury from fishing tackle.

“A late ice-out and therefore late start to nesting means that loons will either have very young chicks or still be on the nest over the July Fourth weekend,” said Harry Vogel, senior biologist/executive director of the Loon Preservation Committee. “In either case, it’s imperative that we give them some space to minimize disturbances at these very vulnerable times in their life cycles.”

The common loon, a threatened species in New Hampshire and federally protected, is a striking, black-and-white migratory bird with red eyes that is found on lakes and large ponds in northern North America and parts of Greenland and Iceland. An adult loon will let people know when it’s distressed: Craning its neck low over the water, thrashing about in the water, or vocalizing. Those are signs they need more space.

Emily Preston, a wildlife biologist with the state’s Fish and Game Department, said motorboats get a lot of the blame for disturbing the birds, but paddle boats like kayaks and canoes, because they can get closer to the nests, actually can be a greater threat. She urges people to observe loons – and all wildlife – from afar.

“If they are looking at you, you are too close,” she said.

Last year, the Loon Preservation Committee recorded 157 loon chicks hatched, but nearly a quarter of them did not survive.

The committee says studies indicate that a minimum breeding success rate of 0.48 surviving chicks per loon pair is needed to maintain the loon population over the long

New Hampshire’s loons have achieved that rate in only two out of the last eight years.

Preston said the research the preservation committee has done for more than three decades is critical to protecting a bird that has cultural and ecological significance in the state.

“It’s a great partnership and we’re fortunate to have an organization like that that has really been in the forefront of loon research and loon monitoring,” she said.

Fish and Game investigates when loons are harmed, such as the shooting of two loons in May, and works with anglers and boaters to minimize human impact on the birds.

“They’re one of those wildlife species that everybody loves,” she said. “They’re beautiful and their calls are amazing.”

The annual Loon Census will take place on Saturday, July 19, which gives the commission a “snapshot” on loon productivity throughout the state and helps it discover new territories.